1. Field of the Invention
The invention relates to a method of producing finely divided, stable oil-in-water emulsions of organopolysiloxanes by condensation and/or polymerization of lower molecular organosilicon compounds in finely divided form in the presence of emulsifiers and condensation and polymerization catalysts.
2. Field of the Invention
Emulsions of organopolysiloxanes in water can be produced by emulsifying organopolysiloxanes of the desired chemical structure and the required viscosity with the help of emulsifiers in water. This method can be used especially for organopolysiloxanes of low viscosity. There are, however, considerable difficulties with respect to transforming silicones of higher molecular weight, and therefore of higher viscosity, into an emulsion.
The preferred method of the state of the art for producing finely divided, stable oil-in-water emulsions of organopolysiloxanes consists therefore of transforming lower molecular organosilicon compounds into an emulsion and condensing and/or polymerizing the organosilicon compounds in the disperse phase of the emulsion.
For example, a method is described in German Auslegeschrift 14 95 512 for producing stable organopolysiloxane emulsions by polymerizing and/or copolymerizing organopolysiloxanes, which optionally are produced in situ and which are built up essentially of units of the general formula ##EQU1## (R being hydrogen or a monofunctional, optionally halogenated hydrocarbon radical, n has an average value of 1 to less than 3),
and/or silcarbanes of the general formula EQU HO(R).sub.2 SiQSi(R).sub.2 OH (II)
(Q being a bifunctional hydrocarbon radical with fewer than 15 carbon atoms, which is possibly interspersed with ether oxygen atoms and is linked to the silicon atoms by Si-C bonds), PA1 (R' being a monofunctional hydrocarbon radical with at least 6 carbon atoms) PA1 (R being hydrogen atoms or monofunctional, optionally halogenated hydrocarbon radicals, Q being bifunctional hydrocarbon radicals with fewer than 15 carbon atoms, optionally interspersed with ether oxygen atoms, the hydrocarbon radicals being linked to silicon atoms by carbon atoms; n=1, 2 or 3 or has an average value between 1 and 3), PA1 (R' is a monofunctional, aliphatic, hydrocarbon radical with at least 6 carbon atoms). PA1 (a) first dispersing the amount of emulsifier required for obtaining a stable emulsion in an amount of water equal to 0.5 to 3 times the weight of the emulsifier; PA1 (b) adding the amount of organosilicon compound which is to be emulsified to this dispersion and homogenizing the mixture by the action of high shear forces until a uniform, transparent to slightly opaque paste is formed, and PA1 (c) when the desired molecular weight is reached, stirring the paste with the remaining water, with little shear in a known manner into an emulsion; PA1 R.sup.2 and R.sup.3 are the same or different and represent an alkyl or a hydroxyalkyl radical with 1 to 4 carbon atoms, PA1 x=2 or 3 and PA1 y=1, 2, 3 or 4.
or dihydroxydiphenylsilanes in an aqueous medium in finely divided form and in the presence of catalysts. This method is characterized by the fact that sulfonic acids having the formula EQU R'C.sub.6 H.sub.4 SO.sub.3 H (III)
is used as the catalyst.
German Auslegeschrift 15 70 451 discloses a method for producing stable organopolysiloxane emulsions by polymerizing and/or copolymerizing organopolysiloxanes having units of the general formula ##EQU2## and/or silcarbanes of the general formula EQU HO(R.sub.2)SiQSi(R).sub.2 OH (II)
in an aqueous medium in finely divided form and in the presence of catalysts. The catalysts used in this method are alkyl hydrogen sulfates of the general formula EQU R'OSO.sub.2 OH (III)
It is pointed out in this Auslegeschrift that the prior emulsification of the organosilicon compounds is not essential for the method claimed there since emulsification and polymerization would take place practically simultaneously.
In practice, the condensation and/or polymerization of lower molecular organosilicon starting compounds in emulsion form has become the generally accepted method for producing finely divided oil-in-water emulsions of organopolysiloxanes. It is, however, a serious disadvantage of this method that the condensation and/or polymerization must be carried out in the presence of large amounts of water and that therefore the use of correspondingly large stirrer equipped vessels is required. In addition, a relatively long time is required, especially in the case of condensation reactions, in order to reach the desired molecular weight, so that the space/time yield of such methods is unsatisfactory.